Thermal air flow rate measuring apparatus and its flowmeter and internal combustion engine and thermal air flow rate measuring method using it

ABSTRACT

A thermal air flow rate measuring apparatus of great precision wherein sensitivity is enhanced by sensors having different output characteristics and an operating device employing a digitized signal. The sensitivity and temperature can be corrected easily depending on the flow direction of fluid. The measuring apparatus includes at least one heating resistor disposed in a gas fluid, temperature detecting resistors formed at an upstream part and a downstream part of the heating resistor in the flow direction of the fluid, a device for outputting at least two signals relating to the flow rate of the fluid, a quantizing device for quantizing the output values, and an operating device for operating the flow rate based on the quantized signals.

TECHNICAL FIELD

The present invention relates to a novel thermal air flow rate measuringapparatus and a novel thermal air flow rate measuring method, and to aninternal combustion engine using the thermal air flow rate measuringapparatus and a thermal air flow rate measuring method suitable fordetecting an intake air flow rate of the internal combustion engine.

BACKGROUND ART

As an air flow rate apparatus for measuring an intake air flow ratearranged in an electronically controlled fuel injection unit of aninternal combustion engine in a vehicle or the like, air flow ratemeasuring apparatuses of thermal type have been widely used because ofcapability of directly detecting a mass air flow rate. Therein, itsheating resistor is constructed by winding a platinum wire around abobbin and then coating the wire with glass, or by forming a thin filmresistor on a ceramic substrate or a silicon substrate.

As the methods of detecting a flow rate, there are a type in which aheating resistor is heated up to a given temperature and a flow rate isdirectly detected from a value of current flowing through the resistorwhen a fluid flows, and a type in which temperature detecting resistorsare arranged in both sides of a heating resistor and a flow rate isdetected from a temperature difference between the temperature detectingresistors.

Particularly in vehicles, in a case of pulsating flow having a largepulsating amplitude of an intake air flow rate and partial reversedflow, which may take place under a low rotation speed and a heavy loadcondition in an engine having four or less cylinders, the conventionalair flow rate measuring apparatus requires an output signalcorresponding to the air flow direction because the accuracy of themeasured flow rate becomes poor. The type, in which temperaturedetecting resistors are arranged in both sides of the heating resistorand an air flow rate is detected from a temperature difference betweenthe temperature detecting resistors, is suitable for detecting an outputsignal under the condition of existing of the reversed air flow becausethe output signal corresponds to the flow direction.

Since each of the above two types has advantages and disadvantagesdepending on the use, a type combining the above both types using ananalog circuit is disclosed in Japanese Patent Application Laid-Open No.9-318412, and in Japanese Patent Application Laid-Open No. 11-51954.That is, since the temperature difference output signal having acomparatively high sensitivity is deteriorated in a high flow rate sidedue to saturation of the sensitivity, the temperature difference outputsignal is output by adding the output signal of the direct detectingtype having low sensitivity in the low flow rate side and highsensitivity in the high flow rate side using a differential amplifier.

As methods of compensating the output signal of temperature differencebetween the temperature detecting resistors having the comparativelygood sensitivity other than the above described method of compensatingthe sensitivity, a method of compensating the output signal by dividingby a temperature rise of a heater is disclosed in Japanese PatentPublication No. 6-63801, and a method of compensating temperature isdisclosed in Japanese Patent Publication No. 6-64080.

In addition, as another method of compensating the output signal oftemperature difference between the temperature detecting resistorsparticularly for vehicles, a method of compensating the output signal bydetecting temperature of a medium is disclosed in Japanese PatentApplication Laid-Open No. 6-160142.

On the other hand, as digitized methods using an A/D converter, a methodof compensating a zero point depending on the output signal of atemperature detecting resistor is disclosed in Japanese PatentApplication Laid-Open No. 6-230021. Further, a method of digitallycompensating temperature is disclosed in Japanese Patent ApplicationLaid-Open No. 11-94620.

In the prior art described above, particularly, as the methods ofcompensating the accuracy of output signal of the temperature differencebetween the temperature detecting resistors, various types mainly usingan analog circuit have been proposed. In the analog circuit, variouskinds of devices different in the measuring range of flow ratecorresponding to the uses are required, and the circuits and theadjustments become complex in order to improve the accuracy. Therefore,these increase the cost. Although the type of digitally compensating thezero point or the type of digitally compensating temperature has beenstudied, adjusting of sensitivity of the whole sensors has not beenconsidered.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a thermal air flow ratemeasuring apparatus and a thermal air flow mater having high accuracy,in which sensitivity is enhanced by an operating means using sensorshaving different output characteristics and employing a digitizedsignal, and the sensitivity and temperature can be corrected easilydepending on the flow direction of fluid, and to provide an internalcombustion engine and a thermal air flow rate measuring method using thethermal air flow rate measuring apparatus.

The present invention is characterized by a thermal air flow ratemeasuring apparatus comprising at least one heating resistor disposed ina gas fluid, temperature detecting resistors formed at an upstream partand a downstream part of the heating resistor in a flow direction of thefluid, an output means for outputting at least two signals relating to aflow rate of said fluid from the heating resistor and the temperaturedetecting resistors, a quantizing means (a digitizing means) forquantizing (digital-converting) the output values, and an operatingmeans for operating the flow rate based on the quantized signals; or athermal air flow rate measuring apparatus comprising an operating meansfor operating the at least two quantized (digital-converted) signalsusing at least two parameters, and a synthesizing and outputting meansfor synthesizing the operated signals and outputting the synthesizedresult; or a thermal air flow rate measuring apparatus comprising anoperating means for operating the at least two quantized(digital-converted) signals using at least two parameters, and an outputmeans for synthesizing the operated signals and outputting thesynthesized result, wherein the two signals relating to the flow rateare signals relating to a heat generating value of the heating resistorand to a temperature difference between the temperature detectingresistors formed at the upper stream part and the downstream part.

Further, the present invention is characterized by a thermal air flowrate measuring apparatus comprising at least one heating resistordisposed in a gas fluid, a flow rate detecting means for detecting aflow rate of the fluid using the heating resistor by driving the heatingresistor at a constant temperature using a temperature compensatingresistor; flow rate detecting means for detecting the flow rate from atemperature difference between temperature detecting resistors eacharranged in both sides of the heating resistor; a quantizing means (adigitizing means) for quantizing (digitizing) a value from the heatingresistor and a value according to the temperature difference; anoperating means for operating the quantized (digital-converted) values;and a correcting means for correcting the operated values.

Further, the present invention is characterized by a thermal air flowrate measuring apparatus comprising at least one heating resistordisposed in a gas fluid; temperature detecting resistors formed at anupper stream part and a downstream part of the heating resistor in aflow direction of the fluid, the temperature detecting resistors beingarranged in multi-stage along a longitudinal direction of the heatingresistor individually at the upstream part and the downstream part; inaddition, an output means for outputting at least two signals relatingto a flow rate of the fluid from the heating resistor and thetemperature detecting resistors; a quantizing means for quantizing theoutput values; and an operating means for operating the flow rater anddirections of the fluid based on the quantized signals.

The present invention is characterized by a thermal air flow ratemeasuring method, which operates a flow rate and a flow direction of agas fluid based on a signal relating to an amount of heat generated byat least one heating resistor disposed in the gas fluid; a signalrelating to a temperature difference between an upstream part and adownstream part of temperature detecting resistors in a flow directionof the fluid, said temperature detecting resistors being formed inmultistage respectively at the upstream part and the downstream part ofthe heating resistor; and a signal relating to a flow difference of thefluid other than the temperature difference, or, in addition to these,based on quantized signals obtained by quantizing the signals describedabove.

In other words, the present invention comprises a heating resistor; ameans for detecting a flow rate by driving the heating resistor at aconstant temperature using a temperature compensation resistor; a meansfor detecting a flow rate from a temperature difference betweentemperature detecting resistors by arranging the temperature detectingresistors in both sides of the heating resistor; a quantizing means (adigitizing means) for inputting a signal corresponding to the flow rateobtained from the heating resistor and a signal corresponding to theflow rate obtained from the temperature difference; and a means forquantizing-operating (digital-operating) the both signals to performcorrection and adjustment.

According to the present invention, even in a case where the air flowrate measuring apparatus is used in different measuring ranges, themeasurement accuracy can be improved by using the two flow rate signalsdifferent in the detection principles and easily adjusting the outputsensitivity through the digital optimization operation.

In the present invention, the function of the first or higher orderequation described above is expressed by any one of (q1=a1×f1+b1, q2=f2,. . . ), (q1=f1, q2=a2×f2+b2, . . . ) and (q1=a1×f1+b1, q2=a2×f2+b2, . .. ), and the function for temperature is expressed by (a1=c1×Ta+d1,b1=c2×Ta+d2, . . . ), and the function for the quantized signal isexpressed by (a1=g1×f1+h1, b1=g2×f1+h2, . . . ). A function of thesecond or third order may be employed for each of the above functions.

According to the present invention, even in a case where the air flowrate measuring apparatus is used in different measuring ranges, themeasurement accuracy can be improved by using the two flow rate signalsdifferent in the detection principles and easily adjusting the outputsensitivity through the digital optimization operation.

In a hot-wire type air flow meter for measuring an intake air flow rateof an internal combustion engine used in a vehicle or the like, thepresent invention provides devices different in the flow rate measuringranges corresponding to various uses, and improves the measurementaccuracy by adjusting the total sensitivity of sensors, and simplifiesthe circuit and the adjustment.

By obtaining the air flow meter having high sensitivity and highaccuracy by executing the digital compensation described above, there isthe effect that amount of exhaust gas from an engine of a vehicle can bereduced by optimizing the engine control.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a drive circuit of a thermal air flow ratemeasuring apparatus according to the present invention.

FIG. 2 is a view showing a pattern of a thermal air flow meter having aheating resistor formed on a silicon substrate.

FIG. 3 is a cross-sectional view showing the thermal air flow meterbeing taken on the plane of the line A-B of FIG. 2.

FIG. 4 is a graph showing an example of correction of the characteristicof output voltage versus air flow rate of a thermal air flow meter inaccordance with the present invention.

FIG. 5 is a graph showing the characteristics of output voltage versusair flow rate of the thermal air flow meter with output adjustment andwithout output adjustment.

FIG. 6 is a graph showing an example of operating correction of thecharacteristic of output voltage versus bidirectional air flow rate ofthe thermal air flow meter.

FIG. 7 is a graph showing an example of judging correction of thecharacteristic of output voltage versus bidirectional air flow rate ofthe thermal air flow meter.

FIG. 8 is a graph showing output errors caused by intake air temperatureand an example of the characteristic correction.

FIG. 9 is a graph showing output errors caused by flow rates and anexample of the characteristic correction.

FIG. 10 is a diagram showing a driving circuit of the thermal air flowrate measuring apparatus in accordance with the present invention.

FIG. 11 is a graph showing an example of operating correction of thecharacteristics of output voltage versus bidirectional air flow rate ofthe thermal air flow meter.

FIG. 12 is a graph showing an example of judging correction of thecharacteristics of output voltage versus bidirectional air flow rate ofthe thermal air flow meter.

FIG. 13 is a diagram of a driving circuit of the thermal air flow ratemeasuring apparatus in accordance with the present invention.

FIG. 14 is a diagram of a driving circuit of the thermal air flow ratemeasuring apparatus in accordance with the present invention.

FIG. 15 is a graph showing output errors caused by intake airtemperature and by substrate temperature and an example of thecharacteristic correction.

FIG. 16 is a block diagram showing an example of operating correctionand output of output-switching.

FIG. 17 is graphs showing an example of the characteristics of sensoroutput versus air flow rate.

FIG. 18 is a block diagram showing an example of operating correctionand output of output-switching.

FIG. 19 is graphs showing the conversion characteristics of air flowrate versus analog-digital converted input value.

FIG. 20 is graphs showing an example of the characteristics of sensoroutput versus air flow rate.

FIG. 21 is a block diagram showing an example of operating correctionand switched output after conversion to air flow rate.

FIG. 22 is a graph showing an example of the characteristics of sensoroutput versus air flow rate.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

FIG. 1 is a diagram showing a drive circuit of a thermal air flow ratemeasuring apparatus according to the present invention. A hot-wire drivecircuit 1 is connected to a power source 101 to output a signalcorresponding to an air flow rate. The hot-wire drive circuit 1comprises a Wheatstone bridge composed of a heating resistor 211 a, atemperature compensation resistor 211 c and resistors 13, 14 and 17, andis constructed in such a manner that current flowing through the heatingresistor 211 a can be controlled by a differential amplifier 15 and atransistor 16 to make an electric potential difference between themidpoints of the bridge zero. When the heated temperature of the heatingresistor 211 a is low, an output of the differential amplifier 15becomes large so as to further heat up the heating resistor 211 a. Bythis construction, the resistance value of the heating resistor 211 a iscontrolled at a constant value independently of the flow rate, that is,the current flowing through the heating resistor 211 a is controlled soas to keep the temperature at a constant value. At that time, as for thesignal of the heating resistor 211 a corresponding to the air flow rate,a voltage signal V2 is obtained by converting the current flowingthrough the heating resistor 211 a to a voltage by the resistor 13 andinputted to a digital correction circuit 220.

Therein, the heating resistor 211 a may be constructed, for example, byforming a thin film or a thick film made of platinum or tungsten as aheat-generator on a glass plate or a ceramic substrate. Particularly,the heating resistor 211 a is a resistor in which a thin film or a thickfilm made of platinum or tungsten as a heat-generator, or apoly-silicone resistor, or a single-crystal silicon resistor is formedon a semiconductor substrate made of silicon or the like.

The heating resistor 211 a is disposed inside an intake air passage ofan internal combustion engine for a vehicle etc to obtain the voltageoutput V2 corresponding to a flow rate of air flowing in the intake airpassage.

On the other hand, an output corresponding to a direction of flow can beobtained from the method that temperature detecting resistors 211 d, 211e, 211 f and 211 g are arranged in the both sides of the heatingresistor 211 a to form a bridge by the temperature detecting resistors211 d, 211 e, 211 f and 211 g, and then a temperature difference betweenthe resistors is detected from a difference between voltage potentialsat midpoints. Therein, the temperature detecting resistors 211 d, 211 e,211 f and 211 g are driven at a constant voltage by a power supplyvoltage Vref1. The method of detecting the temperature differencebetween the resistors is high in the sensitivity in the low flow rateside because of using deferential detection and suitable for detecting abidirectional flow such as back flow, but the sensitivity in the highflow rate side is apt to be limited because of being driven at theconstant voltage.

FIG. 2 is a view showing an example of a pattern in which the heatingresistor 211 a of thin film is formed on a silicon semiconductorsubstrate. The heating resistor 211 a is formed in an oblong shape witha back-and-forth turned pattern of the resistance thin-film wire, andthe temperature detecting resistors 211 d, 211 e, 211 f and 211 g arearranged in the both sides of the heating resistor. The heating resistor211 a and the temperature detecting resistors 211 d, 211 e, 211 f and211 g are arranged in a diaphragm structure part of the siliconsubstrate 211, the diaphragm structure part being formed, for example,by etching the substrate from the back face, and having a small thermalcapacity. A temperature compensation resistor 211 c is arranged at aposition insensitive to temperature rise caused by heat generation ofthe heating resistor 211 a.

The principle of detecting a flow rate from a temperature differencewill be described below in detail. In FIG. 2, air normally flows from Atoward B. Even when there is no air flow, a temperature distribution iscaused in the heater by being heated by the heating resistor 211 a.Under a condition of no air flow, since all the resistance values of thetemperature detecting resistors 211 d, 211 e, 211 f and 211 g are thesame, no output is generated even when the bridge circuit is formed.When air flow takes place, the temperature distributions in the bothsides of the heating resistor 211 a are changed to obtain an outputcorresponding to an air flow rate. In more detail, the resistance valuesof the temperature detecting resistors 211 d and 211 e in the upstreamside of the heating resistor 211 a are decreased because theirtemperatures are decrease, and the resistance values of the temperaturedetecting resistors 211 f and 211 g in the downstream side are increasedbecause their temperatures are increase by receiving heat from theheating resistor 211 a, and thus the produced temperature differencebetween the upstream side and the downstream side can be obtained as thechange in the resistance values.

As described above, by forming the bridge using the plurality oftemperature detecting resistors arranged in the longitudinal directionof the heating resistor 211 a, the sensitivity of detecting thetemperature difference can be improved. From the principle, even whentwo temperature detecting resistors are arranged in the upstream sideand the downstream side, respectively, and a bridge is constructed usingthe two temperature detecting resistors by combining with two resistorsparticularly insensitive to temperature, the same detection can beperformed. However, the sensitivity of output voltage to change in thetemperature detecting resistors decreases lower compared to the casewhere the plurality of temperature detecting resistors are arranged inthe longitudinal direction of the heating resistor 211 a, describedabove. In a case where the temperature dependency of the temperaturedetecting resistors is high, two temperature detecting resistors intotal may be arranged each in the upstream side and the downstream side.However, in a case where the temperature dependency of the temperaturedetecting resistors is high, and accordingly, sufficient outputsensitivity can not be obtained, it is preferable that a plurality of,particularly two, temperature detecting resistors are arrangedrespectively in the upstream side and the downstream side.

FIG. 3 is a cross-sectional view of the resistors formed on the siliconsubstrate. The area having the resistor patterns is constructed so as tohave the thickest substrate. In the present embodiment, the electricpotentials Vb1 and Vb2 of the midpoints of the bridge composed of thetemperature detecting resistors 211 d, 211 e, 211 f and 211 g are alsoinputted to the digital correction circuit 220. The digital correctioncircuit 220 has two analog-digital converters 221 a and 221 b, and readsa voltage corresponding to the flow rate by converting the voltage to adigital value, and adjusts the digital value through operation, and thenobtains an output voltage Vout from a digital-analog converter 224 tooutput the obtained signal to an engine control unit and so on. Therein,the digital correction circuit 220 comprises an operation (calculation)circuit 222 composed of a CPU 222 a, a RAM 222 b and a ROM 222 c; anoscillator 226; a PROM 223; and so on. The PROM 223 may be any memorycapable of storing variations in output sensitivities of individualsensors once or more times as adjusting values, and therefore, is notlimited to an electrically rewritable EEPROM, a flash ROM or the like.

Further, by inputting a voltage Vcc supplied from the external to aninternal power supply/protection circuit 228 as a power supply, a powersupply voltage Vref1 dependent on the external voltage Vcc is used asthe reference voltage by connecting the power supply/protection circuit228 to the analog-digital converters 221 a and 221 b, the digital-analogconverter 224 through switches 225 a and 225 b. The switches 225 a and225 b are for switching between a voltage Vref2 generated by a referencevoltage circuit 229 inside the digital correction circuit 220 and thepower supply voltage Vref1 depending on the external voltage Vccdescribed above. Therein, the analog-digital converters 221 a and 221 bare required to be high accurate because the outputs Vb1, Vb2, V2 etc ofthe bridge circuits are directly inputted. In order to secure the highaccuracy and to make the size of the circuit small, it is preferable toemploy a . . . -type analog-digital converter.

In the present embodiment, the analog-digital converters are providedseparately for digitizing the voltage signal V2 obtained by convertingthe current flowing through the heating resistor 211 a to a voltageusing a resistor 13 and for digitizing the electric potentials Vb1 andVb2 of the midpoints of the bridges composed of the temperaturedetecting resistors 211 d, 211 e, 211 f and 211 g showing a temperaturedifference corresponding to a flow rate. The reason is that both of theprinciples for detecting flow rate are different from each other, andthat each of the constructions can be easily optimized.

The voltage signal V2 is for controlling the bridge voltage of thehot-wire drive circuit 1 by feedback, and the output is independent ofthe power source voltage Vcc of the digital correction circuit 220 etc.Since an independent reference voltage is, therefore, required for theanalog-digital conversion, the reference voltage Vref2 is provided toapply to the analog-digital converter 221 b as the reference.

On the other hand, although the temperature detecting resistors 211 d,211 e, 211 f and 211 g are driven at a constant voltage by the powersupply voltage Vref1, the electric potentials Vb1 and Vb2 of the bridgemidpoints are increased and decreased by fluctuations of the powersupply voltage Vref1. One of the methods of removing this phenomenon isthat the power supply voltage Vref1 is used as the reference voltage ofthe analog-digital converter 221 a, and at the digital conversion, aread value is changed similarly to the fluctuations of the power supplyvoltage Vref1. Particularly, the present embodiment is constructed sothat the reference voltage of the analog-digital converter 221 a can beswitched by providing the switch 225 a. When the fluctuations in thepower supply voltage is very small, a reference voltage Vref2 of areference voltage circuit 229 may be used for the reference voltage ofthe analog-digital converter 221 a.

Further, the digital-analog converter 224 is similarly constructed sothat the reference voltage can be changed by the switch 225 b. Thereason is that the reference can be freely selected when an analog valueis used in the interfacing. In a case where the reference voltage of theanalog-digital converter in the side of a connected control unit and thevoltage Vcc supplied from the external are similar to each other orfluctuate in synchronism with each other, the power supply voltage Vref1is used as the reference. In a case where there is no relation betweenthe reference voltage of the analog-digital converter in the controlunit side and the voltage Vcc, the independent reference voltage Vref2is selected to make matching with the corresponding control unit easyand to make an error due to mismatching of the analog interface smaller.

By constructing the digital correction circuit 220 as described above,the output sensitivity can be improved, and an air flow meter easy inadjustment can be obtained. The detailed operation will be describedbelow, referring to FIG. 4. In FIG. 4, the characteristic of outputversus flow rate obtained from the voltage signal V2 by converting thecurrent flowing through the heating resistor 211 a, described above, isexpressed by a curve f1, and the characteristic output versus flow rateobtained from the voltage difference dV between the electric potentialsVb1 and Vb2 of the bridge midpoints, which shows the temperaturedifference corresponding to the flow rate obtained by the temperaturedetecting resistors 211 d, 211 e, 211 f and 211 g, is expressed by acurve f2.

Since the heating current of the heating resistor 211 a is flowing evenin the condition of zero flow, the output characteristic curve f1becomes an offset output voltage characteristic curve which does notpass through the origin. The zero point of the output characteristiccurve is apt to fluctuate due to natural convection under self-heatingin the condition of zero flow, but the output characteristic curve doesnot saturate in the high flow rate region within a range allowed by thepower supply voltage. Therefore, in a case of using the heating resistor211 a having a small heat capacity, the sensitivity, particularly, inthe low flow rate side is degraded, but the sensitivity in the high flowrate side is high.

On the other hand, the output characteristic curve f2 ideally passesthrough the origin at the zero flow because the output voltage is thedifference between the electric potentials at the bridge midpoints. Thesensitivity, particularly, from the zero flow to the low flow rate sideis high, but the output voltage in the high flow rate side changessmaller to saturate because the difference between temperatures of theresistors becomes small.

In order to actually deal with the characteristics described above, azero-span adjustment, in which the zero point is adjusted by amplifyingit using a differential amplifier or the like, is generally performedthrough an analog method. By doing so, the sensitivity characteristicmay be improved in appearance, but the essential sensitivities of theoutput voltage characteristics f1 and f2 are not changed. In otherwords, there are the contradicting characteristics that thecharacteristic f1 has the low sensitivity in the low flow rate but thehigh sensitivity to the high flow rate side, and that the characteristicf2 has the high sensitivity to the low flow rate but the low sensitivityin the high flow rate side. In order to improve these characteristics,it can be considered that the characteristics are changed using ananalog operating (calculating) circuit composed of differentialamplifiers etc. However, performing of complex analog operation(calculation) to compensate the sensitivities and performing ofadjustment in analog ways to compensate differences among the individualsensors make the adjusting circuits and the adjusting methods complex toincrease the apparatus cost.

The object to solve the above-described problems can be attained byperforming digital operation (calculation) using the digital correctioncircuit 220 described above. In the concrete, the sensitivities of theoutput characteristics f1 and f2 are individually corrected usingfunctions of the first or higher order equation.q1=a1.f1+b1  (Equation 1)q2=a2.f2+b2  (Equation 2)

Then, the above sensitivity-corrected results are multiplied together.q3=q1.q2  (Equation 3)

As the result, it is possible to obtain a better sensitivitycharacteristic from the low flow rate side to the high flow rate sidecompared to the essential sensitivities of the output characteristics f1and f2. As shown in FIG. 5, in order to actually use the calculatedresult of (Equation 3), further adjustment of the output level isrequired at interfacing.q4=ga.q3+off=ga.(q1.q2)+off  (Equation 4)=ga.((a1.f1+b1).(a2.f2+b2))+off=(ga.a1.a2.f1.f2)+(ga.a1.b2.f1)+(ga.a2.b1.f2)+(ga.b1.b2+off)(A.f1.f2)+(B.f1)+(C.f2)+D  (Equation 5)

where, A=ga.a1.a2, B=ga.a1.b2, C=ga.a2.b1, and D=ga.b1.b2+off.

As described above, by providing the digital correction means, theessential sensitive correction and output correction of the sensors canbe easily performed at a time. The calculation may be performedsuccessively from Equation 1 to Equation 4 described above, or thecalculation may be performed in single processing as shown by Equation5. In the case of Equation 5, if the parameters are calculated inadvance and the results are stored, it is advantageous that number ofvariables can be reduced compared to the case where the correctionparameters are individually stored.

According to the present embodiment, there is the effect that in thecase of using the sensors different particularly in the outputcharacteristics f1 and f2, the sensitivity can be improved by thedigital operating (calculating) means, and number of variables for thesensitivity correction can be reduced to simplify the adjustment.

FIG. 6 is a graph showing an embodiment of correction of the outputvoltage characteristics of the sensors in accordance with the presentinvention. The embodiment is in a case where the digital correctingmeans is used in taking the flowing direction of air flow rate. Thecharacteristic f2 of output versus flow rate obtained from the voltagedifference dV between the electric potentials Vb1 and Vb2 of the bridgemidpoints, which shows the temperature difference corresponding to theflow rate obtained by the temperature detecting resistors 211 d, 211 e,211 f and 211 g, gives an output value having a sign depending on theflowing direction. FIG. 6 shows the sensitivity-corrected outputs q1 andq2 which are obtained by correcting the output characteristics f1 and f2using the above-described functions.

The output q2 of the temperature difference type is a positive outputvalue when the flow rate is positive, and is a negative output valuewhen the flow rate is negative. This can be attained in a case where,for example, the analog-digital converter 221 a of the digitalcorrection circuit 220 is constructed so as to be receivable ofdifferential-inputting and capable of converting a positive/negativeanalog differential input to a digital signal having a sign.Particularly, in a case where the sensitivity is different depending onthe flow direction, the correction of the output characteristics can beoptimized by preparing a plurality of parameters a2 u, b2 u, a2 d and b2d for the parameters a2 and b2 in Equation 2 to change the sensitivitycorresponding to the flow direction.

On the other hand, the output q1 of the direct heating type(heat-generating type) is always a positive output value irrespective ofthe positive or negative flow rate, and accordingly, has no sign. Thiscan be attained in a case where, for example, the analog-digitalconverter 221 b of the digital correction circuit 220 is constructed soas to be receivable of ground-based inputting and capable of convertinga positive analog input to a digital signal having no sign. In thiscase, particularly in Equation 1, the sensitivity is adjusted using theparameters a1 and b1 so that the zero point of q2 and the zero point ofq1 may agree with each other.

In the above case of using the output q2 having a sign of thetemperature difference type and the output q1 having no sign of thedirect heating type, the operation (calculation) of sensitivitycorrection may be also executed using Equation 3, as in the aboveembodiment described above, but the multiplied result q3 needs to have asign.

According to the present embodiment, there is the effect that even inthe case where the output characteristics f1 and f2 are different fromeach other and different in sign such as the outputs with sign and theoutputs without sign, sign-added calculation can be easily executed bythe correction through the digital processing, and the sensitivity canbe corrected irrespective of the flow direction of the flow rate, andaccordingly the performance can be improved.

FIG. 7 is a graph showing the relationship between the sensor outputvoltage and the flow rate when the digital correcting means is used intaking the flow direction of air flow rate into consideration. Theoutput q2 of the temperature difference type can be obtained as a signalwith a sign corresponding to the flow direction, as described above. Onthe other hand, the output q1 of the direct heating type does not havethe sign irrespective of the flow direction. However, in this case,particularly in Equation 1, the sensitivity is adjusted using theparameters a1 and b1 so that the output q1 may exceed the output q2 ofthe temperature difference type in the high flow rate side, and the zeropoint of q2 and the zero point of q1 may agree with each other. Further,by checking the sign attached to the output q2 of the temperaturedifference type, an output −q1, which is obtained by attaching the signto the output q1 of the direct heating type, is prepared when the flowrate is negative.

In order to make the sensitivity in the low flow rate side and thesensitivity in the high flow rate side compatible with each other, it isjudged which is larger, the output q2 of the temperature difference typeor the output q1 of the direct heating type. This is realized by aconditional judgment in which, for example, the larger one is selectedwhen the flow rate is positive, and the smaller one is selected when theflow rate is negative. In this case, the judgment is as follows.q1>0,q2.q1 q3=q2  (Equation 6)q1>0,q1>q2 q3=q1  (Equation 7)q1.0,−q2.−q1 −q3=−q2  (Equation 8)q1.0,−q1<−q1 −q3=q1  (Equation 9)

Therein, the minus symbol expresses an output with a sign. By optimizingthe parameters, the flow rate output q3 selected corresponding to theflow rates can be expressed by a smooth curve having small steps atswitching time. Further, the multiplying processing as shown by Equation3 previously described can be omitted by the judging operation.

According to the present embodiment, there are effects that even in thecase where the output characteristics f1 and f2 are different from eachother and different in sign such as the outputs with sign and theoutputs without sign, the sensitivity can be corrected by the digitalcorrection and judgment means, and accordingly the performance can beeasily improved.

FIG. 8 is a graph showing output errors caused by intake air temperatureand an example of the characteristic correction. This embodiment intendsto improve the temperature characteristic particularly when the outputcharacteristics f1 and f2 are used by combining differentcharacteristics. In considering output errors when temperature of theintake air is changed from normal temperature, an output ft1 of thedirect heating type (heat-generating type) is likely to have a positivetemperature characteristic to the intake air temperature because theheating temperature is increased corresponding to the temperature ofintake air. On the other hand, an output ft2 of the temperaturedifference type is likely to have a negative temperature characteristicwhen the temperature detecting resistors are driven by a constantvoltage. Among these temperature characteristics, the characteristic ofthe output ft1 of the direct heating type can be changed by changing thetemperature compensation resistor 17 in the bridge. In that case,however, the adjustment becomes complex because the temperaturecharacteristics are not always uniform. In order to solve this problem,the temperature characteristics can be easily improved by executingdigital operating correction to change an error ratio to eachtemperature characteristic.

That is, in Equation 1 and Equation 2 previously described, each of theparameters can be set according to a ratio of change to temperature ofintake air. For example, assuming that the output ft1 of the directheating type is opposite in polarity to and twice as large as the outputft2 of the temperature difference type, characteristics qt1 and qt2having temperature characteristics opposite to each other are obtainedby adjusting the parameters of Equation 1 and Equation 2. By operatingthese using Equation 3, a characteristic qt3 having a good intake airtemperature characteristic can be obtained. The parameters of Equation 1can be corrected to the intake air temperature Ta, for example, asdescribed below.a1=c1.Ta+d1  (Equation 10)b1=c2.Ta+d2  (Equation 11)

According to the present embodiment, there are effects that even in thecase where the output characteristics f1 and f2 are different from eachother and the temperature characteristics are different each other, thetemperature characteristic performance can be corrected by the digitalcorrection means.

FIG. 9 is a graph showing output errors caused by flow rates and anexample of the characteristic correction. This embodiment intends toimprove the characteristic of flow rate dependency particularly when theoutput characteristics f1 and f2 are used by combining differentcharacteristics. The figure shows the states of changes from the basiccharacteristic of the output corresponding to the flow rate caused bythe surrounding temperature, variations in the devices etc. In general,errors in both of the output fe1 of the direct heating type and theoutput fe2 of the temperature difference type become large in the lowflow rate side. The reason is that an allowable amount to variancedecreases as the flow rate becomes smaller because of using a relativeerror for the evaluation, and therefore, the ratio of error increaseseven when the variance in appearance is the same. Even in such a case,the flow rate dependency can be improved by adjusting the parameterssimilar to the case of the correction of the intake air temperaturedescribed above. For example, characteristics qe1 and qe2, whichminimize the flow rate dependency of the output fe1 of the directheating type to the output fe2, are obtained. By operating these usingEquation 3, a characteristic qe3 having a good flow rate dependency canbe obtained. The parameters of Equation 1 can be corrected to the outputf1 of the direct heating type as described below.a1=g1.f1+h1  (Equation 12)b1=g2.f1+h2  (Equation 13)

By calculating parameters optimum to each of the characteristics inadvance and then executing the digital correction using the parametersoptimum to each of the sensors, as described above, it is possible toobtain an air flow meter having optimum sensitivity, a good intake airtemperature characteristic and a good flow rate dependency.

According to the present embodiment, there are effects that by using thesensors different particularly in the output characteristics f1 and f2and optimizing the individual use condition of the sensors using thedigital correction means, it is possible to obtain an air flow meterhaving optimum sensitivity, a good intake air temperature characteristicand a good flow rate dependency.

There is a remarkable effect that in the case of using the sensorsdifferent particularly in the output characteristics f1 and f2, thesensitivity can be improved by the digital operating means, and numberof variables for the sensitivity correction can be reduced to simplifythe adjustment. At the same time, there is the effect that thesensitivity correction and the temperature correction according to theflow direction can be easily executed to improve the performance.Further, there is the effect that when the air flow meter is used forcontrolling an engine of a vehicle, the exhaust gas if the engine can bereduced because the accuracy of measuring the air flow rate is improved.

Embodiment 2

FIG. 10 is a diagram showing a driving circuit of the thermal air flowmeter in accordance with the present invention. This embodiment is anexample in which the reference voltage circuit in the digital correctioncircuit 220 is arranged in the outside, compared to the embodiment ofFIG. 1. The hot-wire drive circuit 1 is connected to the power supply101, and outputs a signal corresponding to an air flow rate. The powersource circuit 5 is also connected to the power supply 101, and avoltage Vref3 is produced by the reference voltage circuit 51. Thevoltage Vref3 is supplied as the electric power to the digitalcorrection circuit 220 and to the bridge circuit composed of thetemperature detecting resistors 221 d, 221 e, 221 f and 221 g.

In the present embodiment, the electric potentials Vb1 and Vb2 of thebridge midpoints of the temperature detecting resistors 221 d, 221 e,221 f and 221 g are inputted to the analog-digital converter 221 c ofthe digital correction circuit 220 as a temperature difference voltageVb3 which is amplified by resistors 32, 33, 34, 35, 36, 37 and adifferential amplifier 31 in taking an offset voltage Voff as thereference.

Further, a voltage signal V2 obtained by converting the current flowingthrough the above-described heating resistor 211 a to a voltage by aresistor 13 and a voltage Vr1 obtained by dividing the applied voltageV1 of the bridge circuit of the hot-wire drive circuit 1 by resistors212 and 213 are also inputted to the analog-digital converter 221 c ofthe digital correction circuit 220. The analog-digital converter 221 cconverts a voltage value corresponding to the flow rate to a digitalvalue in taking the voltage Vref3 generated by the reference voltagecircuit 51 as the reference, and adjusts the digital value throughoperation, and then obtains an output voltage Vout from a digital-analogconverter 224 to output the obtained signal to an engine control unitand so on.

Therein, the digital-analog converter 224 is constructed so as to beswitchable between the voltage Vref3 generated by the reference voltagecircuit 51 and the external voltage Vcc using a switch 225 b. The reasonis that the reference can be freely selected when an analog value isused in the interfacing. In a case where the reference voltage of theanalog-digital converter in the side of a connected control unit and thevoltage Vcc supplied from the external are similar to each other orfluctuate in synchronism with each other, the voltage Vcc is used as thereference. In a case where there is no relation between the referencevoltage of the analog-digital converter in the control unit side and thevoltage Vcc, the independent reference voltage Vref3 is selected to makematching with the corresponding control unit easy and to make an errordue to mismatching of the analog interface smaller.

Therein, since number of input ports becomes large, it is preferablethat instead of using the analog-digital converters 221 a and 221 b, asingle analog-digital converter is used by using a switch. In order tosecure the converting speed and to make the circuit size smaller, ananalog-digital converter of, for example, a successive comparison typemay be used. In this case, the analog-digital converter 221 c isconstructed so as to be receivable of ground-based inputting, andcapable of converting a positive analog input to a digital signal havingno sign.

FIG. 11 is a graph showing an example of operating correction of thecharacteristics of sensor output voltage versus bidirectional air flowrate. By constructing the digital correction circuit 220 as describedabove, the output sensitivity can be improved similarly to the previousembodiment, and it is possible to obtain an air flow meter easy toadjust and having a smaller circuit size. The characteristic of outputversus flow rate obtained from the voltage signal V2 by converting thecurrent flowing through the heating resistor 211 a, described above, isexpressed by f1, and the characteristic output versus flow rate obtainedfrom the temperature difference voltage Vb3 obtained by amplifying theelectric potentials Vb1 and Vb2 of the midpoints of the bridge composedof the temperature detecting resistors 211 d, 211 e, 211 f and 211 g intaking the offset voltage Voff as the reference is expressed by f2.

Therein, instead of using the voltage signal V2, the voltage obtained bydividing the voltage V1 applied to the bridge circuit using resistors212 and 213 may be used for the output characteristic f1. A differentpoint between the voltages V1 and V2 is difference in the temperaturecharacteristic. Although the temperature characteristic is adjusted by aresistor 17, there is an advantage that the voltage V1 is easy to makethe temperature dependency smaller compared to the voltage V2. Further,heated temperature Th of the heating resistor 211 a can be calculated bymeasuring a voltage between the both ends of the heating resistor 211 a,and temperature compensation using the heated temperature Th may beemployed in order to reduce the temperature dependency. In this case,the calculation of each parameter is as follows.a1=c1.Th+d1  (Equation 14)b1=c2.Th+d2  (Equation 15)

The characteristic of output versus flow rate f2 can be obtained byincreasing and decreasing the output corresponding to the flowdirection. The output of the temperature difference type q2 is apositive output when the flow rate is positive to an offset flow rateq0, and a negative input when the flow rate is negative. Particularly,since the output does not have the sign, it is necessary to performcorrection operation taking the offset flow rate q0 into consideration.The output of the direct heating type q1 is always positive when theflow rate is positive and when the flow rate is negative, andaccordingly there is no need to take the flow direction intoconsideration.

In the case of using the output of the temperature difference type q2without sign and offset described above and the output of the directheating type q1 without sign, it is necessary to perform correctionoperation taking the flow direction into consideration.

As an example, sensitivity-corrected q1 and q2 are obtained from theoutput characteristics f1 and f2 by Equation 1 and Equation 2 previouslydescribed. Here, the range where the flow rate is positive is defined asa region a, an output of the temperature difference type in thisoccasion is defined as q2 a, and an output of the direct heating type inthis occasion is defined as q1 a. Further, the range where the flow rateis negative is defined as a region b, an output of the temperaturedifference type in this occasion is defined as q2 b, and an output ofthe direct heating type in this occasion is defined as q1 b. Calculationof the corrected output obtained by multiplying these outputs isexecuted by separating condition according to the flow rate.q2>q0 q3=q1a.(q2a−q0)  (Equation 16)q2.q0q3=q0−(q1b.(q0−q2b)  (Equation 17)

FIG. 12 is a graph showing an example of judging correction of thecharacteristics of sensor output voltage versus bidirectional air flowrate. As shown in FIG. 12, in this example, the sensitivity correctionis performed by judging magnitude of values using the offset flow rateand the flow direction. Both of the above examples have the same effectas that of the aforementioned embodiment.

According to the present embodiment, there is the effect that even whenthe output characteristics f1 and f2 are different from each other andwithout sign, operation (calculation) equivalent to operation for theoutput characteristics with sign can be performed, and the sensitivitycorrection can be performed irrespective of the flow direction, and theperformance can be improved. Further, there is the effect that thepresent embodiment can be easily realized even if a general-purposemicrocomputer is used because the structure of the digital correctioncircuit 220 becomes simpler.

Embodiment 3

FIG. 13 is a diagram of a driving circuit of the thermal air flow meterin accordance with the present invention. Even if the external voltageVcc is directly inputted to the analog-digital converter 221 c and theoperation of the dependency of the external voltage is executed in thedigital correction circuit 220, as shown in FIG. 13, it is possible toeasily obtain the same effect as the effect of the aforementionedembodiments. Further, by imputing the voltage at the both ends of thetemperature compensation resistor 211 c to the digital correctioncircuit, the intake air temperature can be calculated, and the voltagecan be used for the correction of the intake air temperature and theoutput of the intake air temperature. In the present embodiment, ananalog output of the intake air temperature is realized by providing thedigital-analog converter 224 b. According to the present embodiment, byusing the analog-digital converter having a great number of channels, itis possible to obtain a higher accurate and high-performance air flowmeter.

Embodiment 4

FIG. 14 is a diagram of a driving circuit of the thermal air flow meterin accordance with the present invention. When the bridge voltage isdetected by dividing the voltage, a resistor 211 h having the sametemperature coefficient as the temperature compensation resistor 211 c,a thermistor or the like is used for one of the bleeder resistors, asshown in FIG. 14. By such a construction, the temperature characteristicof the output V1 may be improved in another manner. Different from thetemperature characteristic of the temperature detecting resistors 211 d,211 e, 211 f and 211 g, the temperature dependency of the output V1 canbe more finely pre-changed to a desirable characteristic. By changingthe configuration of the bleeder resistors, the directionalcharacteristic (positive temperature characteristic or negativetemperature characteristic) may be changed. Further, the bleederresistor 213 is arranged inside the digital correction circuit 220 or ina substrate mounting the digital correction circuit 220 though thetemperature compensation resistor 211 h is arranged inside the intakeair passage, and a resistor having a temperature coefficient suitablefor detecting temperature of the substrate is used for the breederresistor 213. By doing so, the effect of temperature of the substratecan be reduced.

FIG. 15 is a graph showing temperature dependencies of the individualresistors to intake air temperature. As shown in FIG. 15, the originaltemperature characteristic vt1 of the direct heating type is improved bythe temperature compensation resistor 211 h to obtain a characteristicvta. On the other hand, an output vt3 compensated on both of the intakeair temperature and the substrate temperature can be obtained from acharacteristic vtm compensated on the substrate temperature.

By operating the above results in the digital correction circuit 220, anoutput having a good temperature characteristic can be obtained. In thepresent embodiment, by providing the resistor 211 h depending on theintake air temperature to pre-compensate the intake air temperature, anair flow meter having a good temperature characteristic can be obtainedeven if an analog-digital converter having a small number of channels.

Embodiment 5

FIG. 16 is a block diagram showing an example of operating correctionand output of output-switching. Description will be made below onsoftware processing of input-and-output in accordance with the presentinvention. Referring to FIG. 16, characteristics of the signals f1 andf2 obtained from the analog-digital converters 311 a and 311 b areimproved by digital operating correction processing 312 using theparameters a1, a2, b1 and b2, as described in the aforementionedembodiment, and thus a characteristic-improved signal q3 is obtained.The signal q3 is converted to an air flow rate by air flow rateconversion processing 313 a, and thus an air flow rate converted signalqv3 is obtained. Therein, the air flow rate is obtained by converting avoltage to a flow rate using, for example, a table called asvoltage-flow rate conversion map. The tables called as voltage-flow rateconversion maps may be prepared for individual sensors, or by using atypical characteristic, correction tables may be separately prepared forindividual sensors. These tables are recorded in a memory element calledas PROM which is writable once or more times, and can hold recordswithout any power source.

In the present embodiment, in regard to the signals, the signal q3 afteroperation and the signal qv3 converted to air flow rate are switchedusing a software switch 316 a which can be operated by a signal from theexternal. In regard to output, an output fout converted to frequency bya pulse conversion processing 314 and a voltage value Vout converted bydigital-analog conversion processing 315 are switched using softwareswitches 316 b and 316 c. By switching as described above, outputs shownin FIG. 17 can be arbitrarily obtained. This function can be easilyrealized by digitization, and a plurality of output interfaces can berealized by the single digital correction circuit 220. Therefore, thepresent embodiment has the effect that commonality of components andaccordingly cost reduction can be achieved.

Embodiment 6

FIG. 18 is a block diagram showing an example of operating correctionand output of output-switching. Referring to FIG. 18, voltages of thesignals f1 and f2 obtained from the analog-digital converters 311 a and311 b are converted to flow rates using tables called as voltage-flowrate maps shown in FIG. 19. Since the two signals are different incharacteristics from each other, the tables are separately prepared. Thesignals qv2 and qv1 converted respectively through air flow rateconversion processing 313 b and 313 c are compensated through operationprocessing 312 to obtain a signal qv3 of which sensitivity of the outputis compensated, similarly to in the aforementioned embodiment, and thenthe digital signal qv3 is converted to a duty of pulse signal throughpulse conversion processing 314. The pulse signal is changed to asmoothed analog signal or a pulse output signal by switching a softwareswitch 316 d, which is switchable by a signal from the external, toselect any one of filters 317 a and 317 b having characteristicsdifferent from each other and to a route without filter. Particularly,by changing the filter characteristic depending on use of the outputsignal, an accurate analog output can be obtained. Since therelationship between the accuracy and the response generally becomestrade-off when such a pulse signal is filter-converted, thedigitalization can easily cope with a case of requiring high accuracyand a case of requiring a high response. FIG. 20 is graphs showing anexample of the output characteristics. Referring to the graphs, both ofthe duty and the output voltage have a similar linear relationship ofoutput signal versus flow rate. From the above results, the presentembodiment has the effect that highly accurate outputs can be obtainedat low cost.

Embodiment 7

FIG. 21 is a block diagram showing an example of operating correctionand switched output after conversion to air flow rate. Another kind ofinput-output software processing will be described below. Referring toFIG. 21, voltages of the signals f1 and f2 obtained from theanalog-digital converters 311 a and 311 b are converted to flow ratesusing tables called as voltage-flow rate maps shown in FIG. 19. Sincethe two signals are different in characteristics from each other, thetables are separately prepared. The signals qv2 and qv1 convertedrespectively through air flow rate conversion processing 313 b and 313 care compensated through operation processing 312 to obtain a signal qv3of which sensitivity of the output is compensated.

Then one of the three different air flow rates qv1, qv2 and qv3 isselected by a software switch 316 e, which is switchable by a signalfrom the external, to be processed through digital-analog conversionprocessing 315. Thus, one of the three flow rates can be obtained as avoltage analog value Vout. FIG. 22 shows the output characteristics. Inthe operation (calculation) processing 312, interrelation among the twoflow rate signals qv2 and qv1 and the output qv3 processed through theoperation processing can be adjusted by preparing a plurality ofcorrection parameters k1, k2, k3, k4, . . . This is particularlyeffective for adjusting of the output, etc. One of the examples will bedescribed below. The signals qv2 and qv1 having different sensitivitycharacteristics and different temperature characteristics in the initialcharacteristics are read as analog values using the software switch 316e, and then the signal qv3 corrected using the correction parameters a1,a2, b1, b2, k1, k2, k3, k4, . . . is obtained. Particularly when thesignals qv2 and qv1 are dispersed, extraction of the parameters becomeseasy. Therefore, signals having higher accuracy against sensitivity andtemperature can be obtained.

In this processing, since the signals qv2, qv1 and qv3 are separatelyobtained particularly when the characteristics are changed by fouling,the correction of errors and the re-adjustment can be performed easily,and the long-term characteristics can be compensated. In the presentembodiment, highly accurate sensors can be provided at low cost by thehigher-level adjustment.

Since an air flow meter having high sensitivity and high accuracy can beobtained by the digital correction described above, there is the effectthat engine control for a vehicle can be optimized to reduce exhaust gasfrom the vehicle.

According to the present invention, it is possible to obtain a thermalair flow rate measuring apparatus and a thermal air flow mater havinghigh accuracy, in which sensitivity is enhanced by an operating meansusing sensors having different output characteristics and employing adigitized signal, and the sensitivity and temperature can be correctedeasily depending on the flow direction of fluid, and to provide aninternal combustion engine and a thermal air flow rate measuring methodusing the thermal air flow rate measuring apparatus. Further, since anair flow meter having high sensitivity and high accuracy can be obtainedby the digital correction described above, there is the effect thatengine control for a vehicle can be optimized to reduce exhaust gas fromthe vehicle.

1. A thermal air flow rate measuring apparatus comprising at least oneheating resistor disposed in a gas fluid; temperature detectingresistors each formed at an upstream part and a downstream part of saidheating resistor in a direction of said fluid; means for outputting atleast two signals relating to a flow rate of said fluid from saidheating resistor and from said temperature detecting resistors; meansfor quantizing said output values; means for operating said at least twoquantized signals using at least two parameters; and a means forsynthesizing operated signals and outputting the synthesized result,wherein said two signals relating to said flow rate are signals relatingto a heat generating value of said heating resistor and to a temperaturedifference between said temperature detecting resistors formed at theupstream part and the downstream part and wherein a plurality of saidquantized signals is adjusted by a plurality of parameters expressed bya function of at least a first order equation, and said adjusted signalsare individually multiplied as output.
 2. A thermal air flow ratemeasuring apparatus comprising at least one heating resistor disposed ina gas fluid; temperature detecting resistors formed at an upstream partand a downstream part of said heating resistor in a flow direction ofthe fluid; means for outputting at least two signals relating to a flowrate of said fluid from said heating resistor and from said temperaturedetecting resistors; means for quantizing said output values to producequantized signals; and means for operating said flow rate and adirection of said fluid based on said quantized signals, wherein saidtemperature detecting resistors are arranged in multistage along alongitudinal direction of said heating resistor individually at saidupstream part and said downstream part and wherein a plurality of saidquantized signals is adjusted by a plurality of parameters expressed bya function of at least a first order equation, and said adjusted signalsare individually multiplied as output.
 3. A thermal air flow ratemeasuring apparatus comprising at least one heating resistor disposed ina gas fluid; temperature detecting resistors formed at an upstream partand a downstream part of said fluid with respect to said heatingresistor; means for outputting at least two signals relating to a flowrate of said fluid from said heating resistor and from said temperaturedetecting resistors; means for quantizing said output values asquantized signals; means for operating said flow rate based on saidquantized signals using at least two parameters, wherein at least one ofsaid quantized signals is adjusted by a plurality of parametersexpressed by a function of the first or higher order equation, and saidplurality of adjusted signals are individually multiplied to be output.4. A thermal air flow rate measuring apparatus according to claim 3,wherein at least one of the signals quantized by said quantizing meansis a sign relating to a flowing direction of said fluid, and saidfunction is selected depending on said sign, and signals adjusted byadding said signs to said quantized signals make a plurality of flowingdirections of said fluid detectable.
 5. A thermal air flow ratemeasuring apparatus according to claim 4, wherein at least one of thequantized signals by said quantizing means has a reference point inregard to a flowing direction of said fluid, and said function isselected depending on magnitude of the signals with respect to saidreference point, and said signals adjusted by adding said signs to saidquantized signals are used.
 6. A thermal air flow rate measuringapparatus according to claim 3, wherein at least two of the quantizedsignals by said quantizing means are adjustable by said plurality ofparameters and external signals.
 7. A thermal air flow rate measuringapparatus comprising at least one heating resistor disposed in a gasfluid; temperature detecting resistors formed at an upstream part and adownstream part of said fluid with respect to said heating resistor;means for outputting at least two signals relating to a flow rate ofsaid fluid from said heating resistor and from said temperaturedetecting resistors; means for quantizing said output values asquantized signals; and means for operating said flow rate based on saidquantized signals using at least two parameters, wherein at least one ofthe quantized signals by said quantizing means is adjusted by saidplurality of parameters each expressed by a function of the first orhigher order equation, and magnitude of said plurality of adjustedsignals is judged to output said signal having the larger magnitude. 8.A thermal air flow rate measuring apparatus comprising at least oneheating resistor disposed in a gas fluid; temperature detectingresistors formed at an upstream part and a downstream part of said fluidwith respect to said heating resistor; means for outputting at least twosignals relating to a flow rate of said fluid from said heating resistorand from said temperature detecting resistors; means for quantizing saidoutput values as quantized signals; and means for operating said flowrate based on said quantized signals using at least two parameters,wherein at least one of said parameters is a function relating totemperature, at least one of the at least two parameters is processedarithmetically by applying a function of at least a first order equationand wherein the air flow signal is obtained arithmetically as thefunction relating to the temperature.
 9. A thermal air flow ratemeasuring apparatus comprising at least one heating resistor disposed ina gas fluid; temperature detecting resistors formed at an upstream partand a downstream part of said fluid with respect to said heatingresistor; means for outputting at least two signals relating to a flowrate of said fluid from said heating resistor and from said temperaturedetecting resistors; means for quantizing said output values asquantized signals; and operating means for operating said flow ratebased on said quantized signals using at least two parameters, whereinsaid quantizing means is composed of a plurality of quantizing deviceswhich are set independently of a reference voltage to be used as areference of quantization.
 10. A thermal air flow rate measuringapparatus according to claim 9, wherein at least one of said pluralityof quantizing devices is means for executing quantization with signhaving a differential input port.
 11. A thermal air flow rate measuringapparatus according to claim 9, wherein said quantized signals arepre-converted to air flow rates and then operated using said at leasttwo parameters, and an operated value operated using said at least twoparameters and individual air flow rates values of converted air flowrates are selectably output by an external signal.
 12. A thermal airflow rate measuring apparatus according to claim 11, wherein saidselected output is obtained by pulse-converting said quantized digitalvalue and then analog-converting said pulse-converted value, and filtersare selectably used when said pulse-converted value is analog-converted.13. A thermal air flow rate measuring apparatus comprising at least oneheating resistor disposed in a gas fluid; temperature detectingresistors formed at an upstream part and a downstream part of said fluidwith respect to said heating resistor; means for outputting at least twosignals relating to a flow rate of said fluid from said heating resistorand from said temperature detecting resistors; means for quantizing saidoutput values as quantized signals; and operating means for operatingsaid flow rate based on said quantized signals using at least twoparameters, wherein at least one of said signals is pre-added with atemperature characteristic by a temperature compensation resistor.
 14. Athermal air flow rate measuring apparatus comprising at least oneheating resistor disposed in a gas fluid; temperature detectingresistors formed at an upstream part and a downstream part of said fluidwith respect to said heating resistor; means for outputting at least twosignals relating to a flow rate of said fluid from said heating resistorand from said temperature detecting resistors; means for quantizing saidoutput values as quantized signals; and operating means for operatingsaid flow rate based on said quantized signals using at least twoparameters, wherein said quantized signals are operated using saidparameters and then converted to air flow rates, and said converted airflow rate values are selectably output by an external signal, andselected output is any one of an analog value obtained byanalog-converting a quantized digital value corresponding to an air flowrate, a frequency obtained by pulse-converting said digital value, or aduty obtained by PWM pulse-converting said digital value.